Magnetic disk files of the high performance type in which one or more magnetic heads are positioned over rapidly-rotating magnetic disks are very sensitive to the presence of solid particles in the area of the disks and particularly in the regions between the disks and the heads. In operation, each head flies a small distance above the surface of the disk and any particle entering the region between a head and a disk can cause damage to the disk. Further, relatively large airborne particles have been found to damage the surface of a disk without involving the head in any way; this damage is caused by the particle striking the surface of the rapidly-moving disk at a shallow angle, thereby ploughing a short furrow in the disk before either bouncing off the disk surface or becoming embedded in the disk surface. There is therefore a requirement for a filtration system to remove as many of these contamination particles as possible.
Prior art disk file filtration systems include that disclosed in GB 2,043,986. This provides a planar filter disposed over a metal plate and arranged such that the variations in air pressure caused by the moving disk generate air flow through the filter. This flow of air through the filter causes airborne particles to be caught and retained in the filter, preventing them subsequently causing any damage to the disk.
Another disk file filtration means is disclosed in IBM Technical Disclosure Bulletin Vol. 24 No. 6 November 1981 p. 2837. This discloses a filter disposed beneath the disk surface which again relies on disk movement to generate air flow through it. Also disclosed are two techniques for increasing the rate of air flow through the filter, the first being baffles to deflect air towards the inlets to the filter and the second being a baffle to reduce the air pressure at the outlets from the filter.
GB 2,076,208 discloses a combination filter assembly for a disk drive wherein one section of the filter is arranged to remove particulate contamination from a recirculating airflow within the disk enclosure (DE) and another section of the filter is arranged to remove particulate contaminants which are borne by air entering the DE through a breather hole in the DE casing.
IBM Technical Disclosure Bulletin Vol. 27 No. 10A March 1985 p. 5587 discloses an auxiliary filter positioned alongside a disk stack and incorporating a shroud for gathering air from a wide angle as it comes off the disks. This air is filtered and then directed towards the servohead so that this head is always operating in a freshly-filtered air flow.